JP4395673B2 - Video display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a video display device, and is suitable as, for example, an HMD (head mounted display) that projects a two-dimensional video displayed on an LCD (liquid crystal display) to an observer's eyes and observes a magnified virtual image thereof. The present invention relates to an image display device.
[0002]
[Prior art]
Japanese Patent Application Laid-Open No. 10-301055 proposes a light-weight and small-sized image display device using a hologram. In this video display device, a reflective hologram having a lens function is provided on the lens surface of the spectacles, and a display unit for emitting video light is provided on the handle of the spectacles. The hologram performs enlarged projection of the image by reflecting the image light from the display unit toward the eyes of the observer. Although the incident angle of the image light with respect to the hologram is larger than the exit angle, the incident angle and the exit angle do not necessarily have to be equal in the reflection by the hologram. This is advantageous in reducing the size of the entire apparatus.
[0003]
[Problems to be solved by the invention]
However, if the incident angle of the image light with respect to the hologram is made larger than the exit angle as described above, the diffraction efficiency becomes worse (see J.Opt.Soc.Am./Vol.71,No7/July 1981 (MGMoharam and TKGaylord) }. When the diffraction efficiency is deteriorated, flare is generated or the brightness of the image is lowered, so that the image quality of the display image is lowered.
[0004]
The present invention has been made in view of such a situation, and an object of the present invention is to provide a video display device capable of displaying high-quality video while being small.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a video display device according to a first aspect of the present invention is a display means for displaying a video, an incident surface that is arranged in front of an observer's eye and on which video light is obliquely incident, and a virtual image of the video. And having a planar diffractive optical surface that is inclined with respect to the incident surface so that the incident angle of the image light is small, and an exit surface that is substantially perpendicular to the line of sight. The diffractive optical surface is made of a material having a high refractive index, diffracts the image light toward the observer's eyes by the diffractive optical surface, and has an optical power for collimating the image light by the diffraction. And a light bending element that bends the image light and reduces the angle of incidence on the diffractive optical surface.
[0006]
According to a second aspect of the present invention, there is provided a video display device according to the first aspect, wherein the light bending element is configured to transmit light from a viewer's front field of view, and light from the front field of view. On the other hand, a correction optical system for correcting so as to cancel the optical action given by the light bending element is provided.
[0007]
According to a third aspect of the present invention, in the configuration of the first aspect, the polarization direction is set so that the image light from the display means is P-type polarized light with respect to the incident surface. And
[0008]
According to a fourth aspect of the present invention, there is provided the video display device according to the first, second or third aspect of the invention, further configured to support the display means and the light bending element and be attachable to the observer's head. A spectacle frame is provided.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an image display apparatus embodying the present invention will be described with reference to the drawings. Note that the same or corresponding parts in the embodiment and the like are denoted by the same reference numerals, and redundant description is omitted as appropriate.
[0010]
<< First Embodiment (FIG. 1) >>
As shown in FIG. 1, the first embodiment bends image light emitted from a reflective LCD (1R) for displaying an image, an LED (2) for illuminating the LCD (1R), and the LCD (1R). The light bending element (3) is configured to guide the observer's eyes (E) and transmit light from the observer's front field of view. Eyeglass-type image with correction optical system (4) that corrects the applied optical action to cancel, and eyeglass frames (5,6) that support each component and can be worn on the observer's head It is a display device. The spectacle frame (5) has a nose pad portion (5a), and supports the light bending element (3), the correction optical system (4), and the like. The spectacle frame (6) has an ear hook (6a), and supports the LCD (1R) and the like.
[0011]
Since this embodiment is a glasses-type head-mounted display device, the entire device is lighter and smaller. When the observer wears this image display device on the head, the light bending element (3) is arranged in front of the eye (E), and the LCD (1R) is located on the side of the eye (E). Will be arranged. The LCD (1R) displays an image on the image plane (1b), and the image plane (1b) is directly illuminated by the light from the LED (2) or indirectly by reflection on the transflective surface (1a). Illuminated. Thus, when the LCD (1R) is illuminated by the illumination means comprising the LED (2) and the transflective surface (1a), image light is emitted from the image surface (1b), and the image light is transmitted through the transflective surface. The light passes through (1a) and is obliquely incident on the incident surface (3a) of the light bending element (3). Note that this entrance surface (3a) is the same surface as the exit surface to the observer's eye (E), and the line of sight of the eye (E) (i.e., when the observer is looking in front with the device attached) It is substantially perpendicular to the line of sight.
[0012]
The polarization direction of the image light from the LCD (1R) is set so as to be P-type polarized light with respect to the incident surface (3a). When the P-type polarized light with respect to the incident surface (3a) is used as image light in this way, the surface reflection at the incident surface (3a) of the light bending element (3) can be reduced. As a result, flare light harmful to the eyes (E) of the observer is suppressed, and a bright image can be obtained with power saving.
[0013]
The image light obliquely incident on the incident surface (3a) is refracted by the incident surface (3a). Of the image light refracted at the incident surface (3a), the one that has passed through the wedge part (3W) of the light bending element (3) or the vicinity thereof is a hologram attached to the inclined surface of the wedge part (3W) ( Incident on 3R). This hologram (3R) is a reflection type diffractive optical element constituting a diffractive optical surface, and acts as a non-axially arranged concave mirror in order to guide an image as a virtual image to the eye (E). Therefore, the image light incident on the hologram (3R) is diffracted toward the observer's eyes (E), and collimated by the diffraction, and exits the incident surface (3a). The image light emitted from the incident surface (3a) enters the pupil (E), and the observer observes the image as a virtual image. The light transmitting part such as the wedge part (3W) constituting the light bending element (3) is made of a material having a higher refractive index than that of the hologram (3R).
[0014]
The diffractive optical surface composed of the hologram (3R) is inclined with respect to the incident surface (3a) so that the incident angle of the image light from the LCD (1R) is small, so that the incident angle is further reduced. The light bending element (3) is configured to refract video light at the incident surface (3a). If the incident angle of the image light with respect to the diffractive optical surface is reduced, the incident angle and the exit angle with respect to the diffractive optical surface can be made equal (regular reflection condition), so that high diffraction efficiency can be achieved, and Optical design is also facilitated. In addition, since the image light from the LCD (1R) is obliquely incident on the incident surface (3a) at a large incident angle, the distance between the light bending element (3) and the LCD (1R) is determined by the observer. It becomes shorter in the line-of-sight direction. Therefore, it is possible to reduce the thickness of the front part of the glasses.
[0015]
The correction optical system (4) is attached to the wedge portion (3W) of the light bending element (3) via the hologram (3R). That is, the light bending element (3) and the correction optical system (4) are in a state of being bonded with the hologram (3R) interposed therebetween, and form a very thin flat plate having a thickness of 5 mm or less. As described above, the light bending element (3) bends the image light from the LCD (1R) and guides it to the viewer's eyes (E), while allowing the light from the viewer's front field to pass therethrough. It is configured. Therefore, when the light from the front view passes through the wedge portion (3W) of the light bending element (3), the light from the front view is bent by the power of the wedge portion (3W). When the wedge portion (3W) is formed of a curved surface, the front field of view is enlarged or reduced by the power of the curved surface. The correction optical system (4) corrects such an optical action so as to cancel. Since the correction optical system (4) cancels the power of the light bending element (3), the observer can observe the front field of view as usual (that is, when the apparatus is not worn).
[0016]
Next, the optical action of the wedge portion (3W) of the light bending element (3) and the hologram (3R) will be described with reference to FIG. Video light from the LCD (1R) (indicated by a broken line in FIG. 5) is obliquely incident on the incident surface (3a) from the air at a large incident angle α1, and is refracted at a refraction angle α2. Since the incident surface (3a) is substantially perpendicular to the line of sight of the eye (E), the angle α1 between the line of sight of the eye (E) and the image light becomes the incident angle with respect to the incident surface (3a). . The image light refracted on the incident surface (3a) passes through the wedge portion (3W) and enters the hologram (3R).
[0017]
Since the hologram (3R) is inclined with respect to the incident surface (3a) by the inclination angle α0, the incident angle of the image light with respect to the hologram (3R) is (α2−α0). The image light is refracted at a refraction angle α3 when incident on the hologram (3R) and is diffracted by the fringe recorded in the hologram (3R). Here, to simplify the drawing, it is assumed that the interface between the hologram (3R) and the correction optical system (4) is a diffractive optical surface, and the image light is diffracted by the diffractive optical surface. The diffracted image light exits from the hologram (3R) at an incident angle α4 and a refraction angle α0 with respect to the wedge part (3W), and then exits the incident surface (3a) substantially perpendicularly and enters the observer's pupil (E). To do.
[0018]
Here, when the refractive index of air is n1, the refractive index of the wedge portion (3W) is n2, and the refractive index of the hologram (3R) is n3, the following formulas (1) to (3) are obtained from the law of refraction. It holds.
n1 · sinα1 = n2 · sinα2 (1)
n2 · sin (α2−α0) = n3 · sinα3 (2)
n3 · sinα4 = n2 · sinα0 (3)
[0019]
In the above equations (1) to (3), when α0 = 14 degrees, α1 = 70 degrees, n1 = 1, n2 = 2, and n3 = 1.5, α3≈α4≈18.8 degrees. That is, diffraction by the reflection type hologram (3R) is performed at an angle close to regular reflection where the incident angle and the exit angle with respect to the diffractive optical surface are equal. Therefore, as shown in J.Opt.Soc.Am./Vol.71,No7/July 1981 by MGMoharam and TKGaylord, high diffraction efficiency can be achieved.
[0020]
Next, for comparison with the first embodiment (FIG. 5), a first comparative example will be given and the optical action of the hologram will be described with reference to FIG. The first comparative example shown in FIG. 6 corresponds to the hologram configuration (configuration in which a hologram is pasted on the spectacle lens surface) proposed in Japanese Patent Laid-Open No. 10-301055 described above. A hologram (11R) is pasted on the substrate (11), and the hologram (11R) and the substrate (11) are arranged substantially perpendicular to the line of sight of the eye (E).
[0021]
Video light (indicated by a broken line in FIG. 6) is obliquely incident on the incident surface (11a) from the air at a large incident angle α1, and is refracted at a refraction angle α5. Since the incident surface (11a) is substantially perpendicular to the line of sight of the eye (E), the angle α1 between the line of sight of the eye (E) and the image light becomes the incident angle with respect to the incident surface (11a). . The image light incident on the hologram (11R) is diffracted by the fringe recorded in the hologram (11R). Here, to simplify the drawing, it is assumed that the interface between the hologram (11R) and the substrate (11) is a diffractive optical surface, and the image light is diffracted by the diffractive optical surface. The diffracted image light exits the incident surface (11a) substantially perpendicularly and enters the observer's pupil (E).
[0022]
Here, assuming that the refractive index of air is n1 and the refractive index of the hologram (11R) is n3, the following formula (4) is established from the law of refraction.
n1 · sinα1 = n3 · sinα5 (4)
[0023]
In the above formula (4), if α1 = 70 degrees, n1 = 1, and n3 = 1.5, then α5 = 38.8 degrees. Since the exit angle from the diffractive optical surface is 0 degree, the diffraction by the reflection hologram (11R) is performed at an angle shifted by 38.8 degrees from the regular reflection angle. Therefore, as shown in J.Opt.Soc.Am./Vol.71,No7/July 1981 by MGMoharam and TKGaylord, the diffraction efficiency is deteriorated.
[0024]
Further, for comparison with the first embodiment (FIG. 5), a second comparative example will be given and the optical action of the hologram will be described with reference to FIG. In the second comparative example shown in FIG. 7, in order to emit image light in the regular reflection direction with the hologram (11R), the hologram (11R) and the substrate (11) are tilted from the state of the first comparative example by an inclination angle α9. It is tilted.
[0025]
Video light (indicated by a broken line in FIG. 7) is obliquely incident from the air on the incident surface (11a) at an incident angle α6 and is refracted at a refraction angle α7. Since the normal of the incident surface (11a) is inclined by an inclination angle α9 with respect to the line of sight of the eye (E), the difference between the angle α1 formed by the line of sight of the eye (E) and the image light and the inclination angle α9 (α1 −α9) becomes the incident angle α6 with respect to the incident surface (11a). The image light incident on the hologram (11R) is diffracted by the fringe recorded in the hologram (11R). Here, to simplify the drawing, it is assumed that the interface between the hologram (11R) and the substrate (11) is a diffractive optical surface, and the image light is diffracted by the diffractive optical surface. The diffracted image light exits from the hologram (11R) at an incident angle α8 and a refraction angle α9 with respect to the incident surface (11a) and enters the observer's pupil (E).
[0026]
Here, assuming that the refractive index of air is n1 and the refractive index of the hologram (11R) is n3, the following formulas (5) and (6) are established from the law of refraction.
n1 · sinα6 = n3 · sinα7 (5)
n3 · sinα8 = n1 · sinα9… ▲ 6 ▼
[0027]
In the above formulas (5) and (6), if α9 = 35 degrees, α1 = 70 degrees, n1 = 1, and n3 = 1.5 (where α6 = α1-α9), α7 = α8 = 22.5 degrees. That is, diffraction by the reflection hologram (11R) is performed at an angle close to regular reflection where the incident angle and the exit angle with respect to the diffractive optical surface are equal. Therefore, as shown in J.Opt.Soc.Am./Vol.71,No7/July 1981 by MGMoharam and TKGaylord, high diffraction efficiency can be achieved. However, if the substrate (11) is tilted by 35 degrees (= α9) in this way, the apparatus becomes larger in the direction of the line of sight of the eye (E). In other words, even if the incident angle is made closer to the exit angle by tilting the spectacle lens with the hologram (11R) attached, the device can be made smaller while ensuring the observation pupil diameter and eye relief at a predetermined viewing angle. It is difficult to make it.
[0028]
<< Second Embodiment (FIG. 2) >>
FIG. 2 shows an optical system portion of the second embodiment. The spectacle frame configuration is the same as that of the first embodiment described above. In this embodiment, a transmissive LCD (1T) is used as display means for displaying an image, and a backlight (2B) is used as illumination means for illuminating the LCD (1T). Further, the curvature of each surface (3a, 3b; 4a, 4b) of the light bending element (3) and the correction optical system (4) is set so as to correct the visual acuity with respect to the observer's eyes (E). Yes. That is, the light bending element (3) and the correction optical system (4) are in a state of being bonded with the hologram (3R) interposed therebetween, and a smooth curved surface is formed by the surface (3a) and the surface (4a). In addition, the surface (3b) and the surface (4b) form a lens shape in which a smooth curved surface is formed. The correction optical system (4) that forms part of the lens shape corrects the optical bending element (3) so as to cancel out the optical action that the light bending element (3) gives only at the wedge part (3W) to the light from the front field of view. At (3W), the light from the front field of view is not bent or the front field of view is not reduced.
[0029]
<< Third Embodiment (FIG. 3) >>
FIG. 3 shows an optical system portion of the third embodiment. The spectacle frame configuration is the same as that of the first embodiment described above. In this embodiment, a curved hologram (3R) is used, and the hologram (3R) has an axis parallel to the normal direction of the plane formed by the folded optical axis (that is, an axis perpendicular to the paper surface). Curved to the center. By using the hologram (3R) curved in this way, the diffraction efficiency for on-axis light and off-axis light can be increased. Also, in order to correct the optical action that the curvature of the wedge part (3W) to which the hologram (3R) is attached has on the light from the front field of view, the correction optical system (4) cancels out the wedge part (3W). Thus, the light from the front view is not bent or the front view is not enlarged. In the third embodiment, since the diffractive optical surface is not planar, the third embodiment is merely a form for reference of the present invention and does not belong to the present invention. .
[0030]
<< Fourth Embodiment (FIG. 4) >>
FIG. 4 shows a fourth embodiment. The feature of this embodiment is that a transmission hologram (3T) is used. According to the first embodiment, except that the reflective LCD (1R) is arranged on the upper front side of the spectacle frame (5) in accordance with the construction of the diffractive optical surface with the transmission hologram (3T). The configuration is almost the same as in the embodiment. Of the image light obliquely incident on the incident surface (3a) from the LCD (1R) and refracted, the image light that has passed through the wedge part (3W) of the light bending element (3) or its vicinity is inclined by the wedge part (3W). Incident on the hologram (3T) affixed to the surface. This hologram (3T) acts as a non-axially arranged convex lens to guide the image as a virtual image to the eye (E). Accordingly, the image light incident on the hologram (3T) is diffracted toward the observer's eyes (E), collimated by the diffraction, and transmitted through the correction optical system (4). The image light emitted from the exit surface (4c) of the correction optical system (4) enters the pupil (E), and the observer observes the image as a virtual image.
[0031]
【The invention's effect】
As described above, according to the present invention, the diffractive optical surface is inclined with respect to the incident surface so as to reduce the incident angle of the image light. An image display device capable of displaying an image with high image quality can be realized. In addition, since it can be realized with a relatively simple configuration, the cost of the apparatus can be reduced.
[Brief description of the drawings]
FIG. 1 is a plan view showing a first embodiment.
FIG. 2 is a plan view showing an optical configuration of a main part of a second embodiment.
FIG. 3 is a plan view showing an optical configuration of a main part of a third embodiment.
FIG. 4 is a longitudinal sectional view showing an essential optical configuration of a fourth embodiment.
FIG. 5 is an optical configuration diagram showing an optical action of a wedge portion of a light bending element and a hologram in the first embodiment.
FIG. 6 is an optical configuration diagram showing an optical action of a hologram in the first comparative example.
FIG. 7 is an optical configuration diagram showing an optical action of a hologram in a second comparative example.
[Explanation of symbols]
1R: Reflective LCD (display means)
1T ... Transmission type LCD (display means)
1a ... Transflective surface
1b Image plane
2 ... LED
2B… Backlight
3 ... Light bending element
3a ... Incident surface
3R: Reflective hologram (diffractive optical surface)
3T ... Transmission hologram (diffractive optical surface)
3W… wedge part
4… correction optics
E ... eyes (eyes)

Claims (4)

Display means for displaying video;
Disposed in front of the viewer's eye, the entrance surface image light is obliquely incident, it guides the eyes of the image as a virtual image, and inclined with respect to the incident surface such that the incident angle of the image light decreases plane A diffractive optical surface and an exit surface substantially perpendicular to the line of sight, made of a material having a higher refractive index than air, and diffracting image light toward the observer's eyes with the diffractive optical surface, An optical power for collimating image light by the diffraction on the diffractive optical surface, bending the image light from the display means, and a light bending element for reducing the incident angle to the diffractive optical surface;
A video display device comprising:   A correction optical system configured so that the light bending element can transmit light from the front view of the observer, and further corrects the optical action of the light bending element with respect to the light from the front view. The video display device according to claim 1, further comprising:   2. The video display device according to claim 1, wherein a polarization direction is set so that video light from the display means becomes P-type polarized light with respect to the incident surface.   4. The video display according to claim 1, further comprising a spectacle frame configured to support the display means and the light bending element and to be mounted on an observer's head. apparatus.

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